Bug sex: the top five most bizarre invertebrate sexual practices

The animal kingdom can be an aggressive place when it comes to
reproduction, with alpha males killing off their counterparts to
ensure their genetic line persists. Invertebrates, however, present
some pretty extreme competition in the stakes for the most bizzare,
rapacious or unusual sexual practices.

To hunt down the weirdest of these interludes, Wired.co.uk
sought out the advice of biologist, insect-lover and Wild Sex presenter Carin
Bondar. In her web series Bondar approaches the subject
matter with a hint of humanisation and a whole lot of
humour: "I love humanising because it gives us a chance to put
examples out there that grab attention," she told Wired.co.uk.

"I enjoy giving them a face and a description. You might want to
call it shock value, but this is all totally real -- there's a lot
of kink going on, so I never get tired of talking about this
stuff."

From eyeball-grabbing to self-castration, here are Bondar's top
five weirdest insect sex stories.

5. Evolutionary arms race: water
striders

Watching water striders skim and skip across a pond is surely a
hypnotic sight. Watch two hop around together under a microscope,
and it quickly becomes clear this dance is anything but hypnotic
for the female.

"In a lot of insects there's a polyandrous mating system whereby
one female mates with several males," explains Bondar. "She can
often get enough sperm for her entire reproductive life from very
few inseminations. But of course males that haven't had a chance to
make a deposit yet will want to get their sperm in there. This
creates a conflict between the sexes and it's beautifully
illustrated in the water strider."

This conflict has taken on the form of an evolutionary arms race
-- one that might seem a beautiful example of nature's battle of
the sexes, but is also a pretty horrific one for the female. As
science writer Ed Yong commented when the University of Toronto recently
revealed the latest terrifying nugget of information about
male water strider tactics, "the worst sex you have ever had pales
in comparison to what female water striders have to put up
with".

Using high-speed cameras and electron microscopes, the team of
evolutionary ecologists uncovered the mystery behind the male water strider's
inordinately spiked antennae, which it uses to grasp and cling on
to the female until she submits to its advances.

"The males have evolved some very sinister grasping structures,"
says Bondar. "They have these very well-crafted antennae that
actually grasp and clamp on to the female's eye, right around her
socket so that he can get on there. It's almost like a wrench."

In one species, the Rheumatobates rileyi, the mature male's
antennae are actually lined with spikey hairs and bend back on
themselves, so they literally do wrench around the eyeball and hook
on.

"They're large, muscular, and fitted with spines and spikes
exquisitely adapted for grasping -- a long way from an insect
feeler," said one of the University of Toronto biologists. Towards
their ends, the antennae actually become singular spikes, which
perfectly fit around the female's eye and use fine hairs to clamp
on. The team found that the Dll gene in
the male of the species had evolved to spur on antennae
adaptation.

The female, however, also has a few tricks. "She has evolved
several anti-grasping structures to be able to turf him off because
it's a big cost for her, ecologically speaking," says Bondar. "He's
not only a monkey on her back, but him being there makes her more
susceptible to predators and takes more of her time away from doing
things like finding food." Carrying the male on her back while she
struggles to kick him off forces the female to expend 20 percent
more energy. Furthermore, when the male actually manages to insert
its appendage into the female, it expands so it locks on and he is
harder to shake off.

Some females have developed elongated spines to help shake off
the males, but even this is not always enough. Enter the genital
shield.

It was discovered in 2009 that females of the Gerris gracilicornis
species can block their reproductive entry point with hard,
chastity belt-style shields. Not to be scuppered, the male has come
up with a shifty tactic based on blackmail. Namely, he bangs his legs on the water's surface while mounted on the
female, drawing attention from predators. In the aptly named paper on the topic, "Male water striders attract predators to
intimidate females into copulation", it was explained that the
threat is basically, "let me have sex with you, and I'll stop
making vibrations on the water's surface, which will otherwise lead
to us both being swallowed by a passing fish". The female is
underneath so is most likely to get eaten -- the male can just let
go and flit away.

"For a male his primary goal is to get his sperm into the next
generation and hers is simply to choose a suitable male," says
Bondar, "but in the water strider I'm not sure there is much choice
going on so it really is a big conflict. It's an ongoing battle --
many more thousands of years from now I wonder what we'll see."